1. Field of the Invention
This invention is concerned with a device which determines the position of an object such as the human finger in a plane, usually for the purpose of providing a human interface with a computer, wherein the interface is adaptable to a large variety of surfaces. The system uses ultrasonic techniques.
2. Brief Description of the Prior Art
Prior art position sensors for computers have included keyboards and specialized CRT screens, as well as (x, y) coordinate sensors which required the use of a stylus. The keyboard systems have used either mechanical switches or various types of touch-sensitive switches, such as capacitive switches. They have, of course, been limited to the specific configuration of the keys of the keyboard, although the functions of the keys could change. Keyboard switches could be used to direct the position of an indication appearing on a CRT screen by causing the indication to move in response to keys pressed. Likewise, a joystick could also be used for remote actuation of an indication on a screen.
Specialized CRT screens typically include conductive portions on the facemask of the screen. The user touches that portion of the screen which displays an indication. That portion must coincide with one conductive segment of the screen. Obviously, the computer program has to be fitted to the number of conductive segments available.
Systems have been developed which use reflected sound waves to determine the position of a stylus. Because of the nature of operation of these prior art devices, diverse objects such as the human finger could not be used and a stylus was required. Furthermore, these systems were not adapted to be placed over a wide variety of surfaces because of the inherent tendency of altered surfaces to alter the echo signals received. These problems are caused by the method of transmitting and receiving signals, as well as by the nature of the transducers used in the prior art which required a specialized environment beyond that of a particular flat surface in a more-or-less rectangular area to one side of the set of transducers. Furthermore, these systems use a transducer for transmitting and two transducers for receiving and cannot be placed inside a frame around the flat surface.
Other devices have been used to detect the positions of a wide variety of objects, using a specialized surface. In these devices, the specialized surface itself reacts to sound wave energy. Clearly, the specialized surface must, at the very least, be placed over another surface in order that another surface be used as a display. Usually, even that is not possible and the display is limited to one surface.